Music Blocks, a fork of Turtle Blocks, is a Free/Libre Software collaboration among numerous contributors. The core ideas behind Music Blocks were developed by Walter Bender and Devin Ulibarri.
Learn more about contributors from here.

There are many ways to contribute: you can create a MB project to share, create some music, write or improve the documentation, report bugs, fix bugs, request new features, or contribute code.
The open list of issues -- bugs and feature requests -- can be found here.
To contribute code, please first fork a copy of Music Blocks GitHub repository. Please follow the guidelines for contributions found here.

There is no specific forum for Music Blocks, but you can raise your questions related to Music Blocks in Sugar Labs IRC channels and also in Sugar Labs email lists. The developers of Music Blocks are frequently on the #sugar IRC channel.

You can Click on the ‘Save Project’ option in Auxiliary toolbar and then you will see the option to ‘Upload to Planet’ in the appearing pop-up. You can add your project to the Planet and share with the other users.

No. You can learn more about music with Music Blocks. If you have no experience with music whatsoever, it may be helpful to read code that others have created. It is also helpful to try examples in the 'Play with Music Blocks' and 'Examples with Music Blocks' sections in this user manual.